Web clamping apparatus

ABSTRACT

An electrically actuable clamping device useful in a web feed apparatus such as a high speed impact printer for preventing movement of the paper during printing. The clamping device comprises a large flat coil structure supported by a plurality of flexure members such as leaf springs, and oriented in a plane extending substantially perpendicular to the plane of the paper. A permanent magnet field is developed perpendicular to the plane of the coil so that when current is driven through the coil, a force is produced which acts to move the coil structure forward to clamp the paper against a pressure plate. The coil current is developed by a closed loop circuit in which a coil structure velocity signal is fed back to enable the coil structure to be moved rapidly, quietly, and without impact or marking between &#39;&#39;&#39;&#39;clamp&#39;&#39;&#39;&#39; and &#39;&#39;&#39;&#39;release&#39;&#39;&#39;&#39; positions. The velocity signal is developed by a transducer including a small coil carried by the large coil structure.

United StatesPatent 1 Helms WEB CLAMPING APPARATUS [75] Inventor: Clifford J. Helms, Woodland Hills,

Calif.

[73] Assignee: Data Products Corporation,

Woodland Hills, Calif.

[22] Filed: June 18, 1971 [21] Appl. No.: 154,573

[ Apr. 9, 1974 Primary ExaminerErnest T. Wright, Jr. Attorney, Agent, or Firm-Lindenberg, Freilich &

Wasserman [5 7] ABSTRACT An electrically actuable clamping device useful in a web feed apparatus such as 'a high speed impact printer for preventing movement of the paper during printing. The clamping device comprises a large flat coil structure supported by a plurality of flexure members such as leaf springs, and oriented in a plane extending substantially perpendicular to the plane of the paper. A permanent magnet field isdeveloped perpendicular to the plane of the coil so that when current is driven through the coil, a force is produced which acts to move the coil structure forward to clamp the paper against a pressure plate. The coil current is developed by a closed loop circuit in which a coil structure velocity signal is fed back to enable the coil structure to be moved rapidly, quietly, and without impact or marking between clamp" and release positions. The velocity signal is developed by a transducer including a small coil carried by the large coil structure.

13 Claims, 5 Drawing Figures PAIENTEUAPR 9:974 I 3.802.546

sum 10; 2

CL IFFOIQD H51. Ms B Y PATENTEDAPR' 9 I974 SHEET 2 0F 2 PAPER FEED AC8 INPUT 1 SiGNAL.

CONTROL). LOGIC PosmoN PULSE.

L f a PAPER FEED \NPUT SK-JNAL \oz lPosmoN PULSE O PAPRR VELOCITY H i 4 I20 I24 c RELEASE COMMAND f I 132 \36 r HOLD COMMAND e VELOCITY aeNAL/ COMMAND GEN OUTPUT +7AMPS PAPER CLAMP Fl OAMPS 7p con. CURRENT -2AMP5 RELEASE N 9 B\AE EAGNAL OUT no HOLD 1'1 l2 EJiAS S\G NAL N {N TACH OUT 6 SWITCH SlGNAL.

CLIFFORD J. HEL/v/ WEB CLAMPING APPARATUS FIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART Impact printers are well known in the data processing field for providing hard copy computer output. Typically, such printers comprise a type surface, such as a character drum or chain, which continually moves past a printing station comprised of a bank of aligned individually actuatable hammers. A paper web and an ink web are disposed between the hammer bank and type surface. The paper is normally stepped one line at a time with a full line being printed between successive paper movements. Printing is accomplished by actuating each hammer at the appropriate time to propel it against the type surface when the character to be printed moves into alignment with the hammer striking face.

In order to increase printing speed, continuing efforts have been made to maximize the speed of both paper and hammer movement. These efforts have resulted in the availability of impact printers capable of printing on the order of 2,000 lines per minute with generally acceptable print quality. It should be apparent that for a given apparatus, as printing speed is increased beyond a certain point, print quality may be degraded. For example, the interval required to step the paper by one line normally represents a significant portion of a print cycle. Thus, the duration of this interval affects the print line rate. Selection of this duration depends somewhat upon the, print quality desired inasmuch as a certain amount of time must be allotted for allowing the paper movement to settle after stepping. If a lower print quality (e.g. slight misregistration of characters) can be tolerated, the settling time selected will be minimal and thus the line rate maximized. If a better print quality is desired, the settling time allotment is increased and the line rate consequently reduced.

Print quality, in terms of registration between characters in a single line, is also affected by how rigidly the paper drive system holds the paper under impact. That is, even if a settling time duration is selected which assures that the paper movement has been completely damped prior to printing, as a practical matter, there is always some degree of compliance and backlash within the elements (e.g. belts, etc.) of the paper drive system. As a consequence of this complicance and backlash, the initial hammer impact against the character drum, after paper settling, may move the paper as the paper is dragged by the continually rotating drum. More particularly, consider the drum surface moving downwardly past the hammer faces. As the hammer striking face impacts against the drum squeezing the paper therebetween, the paper will be dragged downwardly by the drum motion taking up whatever compliance and/or backlash which exists in the paper drive system. As a result, subsequent characters in that line will be printed high relative to the initially printed character.

Efforts have been made in the prior art to utilize simple solenoid actuated clamps to prevent this paper movement. The results of these efforts have been somewhat unsatisfactory because the solenoids are comparatively slow acting and since their use requires a significant additional interval within the print cycle, their effect has been to seriously reduce print line rate. Additionally, such prior art devices often cause paper feed problems (jams) because as a consequence of minimizing clamp movement to minimize actuation time, the

small clearance provided for the paper is sometimes too small to pass folds in the paper, for example.

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide an improved means for controllably clamping a web.

Briefly, a web clamping means is provided in accordance with the present invention comprised of a large coil structure supported for linear movement within a permanent magnet field. More particularly, the coil structure is supported by flexure members such as leaf springs. The coil structure is preferably oriented in a plane extending perpendicular to the plane of the web so that a force developed in response to a current driven through the coil will project the coil structure forwardly to thus clamp the web against an opposed pressure plate. The front edge surface of the coil structure is shaped to conform to the opposed pressure plate surface to hold the web fixed and flat.

In accordance with a significant feature of the present invention, the coil structure is linearly displaced in a controlled manner by employing a closed loop circuit to develop the coil drive current. Moree particularly, a command signal is generated which is summed with a feed back signal representative of coil structure velocity to develop an error signal for producing the coil current.

In accordance with a further feature of the invention, the command signal is shaped so as to controllably reduce the coil structure velocity to substantially zero upon reaching the forward clamp position or the rearward quiescent release" position. As a consequence of reducing the coil structure energy to zero coincident with it reaching its forward and rearward destination positions, it can be moved rapidly without overshooting, without marking the paper, and without producing any substantial noise in crashing against mechanical stops. Further, the foregoing feature enables the clamp to be rapidly moved far enough rearwardly to provide sufficient clearance for paper folds, etc.

In accordance with a still further feature of the invention, the transducer provided to produce a velocity feedback signal is comprised of a small coil carried by the large coil structure and movable in a permanent magnet field. The transducer coil is preferably oriented transverse to the coil structure to minimize inductive coupling therebetween.

In accordance with a still further feature of the invention, means are provided for selectively applying oppositely directed bias currents to said coil to hold said coil structure in either said clamp or release positions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view illustrating a portion of a high speed impact printer incorporating a clamping device in accordance with the present invention;

FIG. 2 is a sectional view taken substantially along the plane 2-2 of FIG. 1;

FIG. 3 is a sectional view taken substantially along the plane 3-3 of FIG. 1;

FIG. 4 is a block diagram of a closed loop control circuit for developing the coil drive current; and

FIG. 5 is a wave form diagram illustrating various signals occurring within the circuit of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now called to FIG. 1 of the drawing which schematically illustrates a portion of a high speed impact printer frequently used as a data processing output device. The printer 10 usually consists of a movable type surface in the form of a drum 12 mounted for rotation about an axis 14. The drum 12 normally has raised alphanumeric characters (not shown) formed in circumferential tracks extending around the drum surface Typically, a drum 12 may have 132 tracks which enables a line of 132 characters to be printed. Positioned opposite to each of the drum tracks is a different hammer 16 in a hammer bank 18. A paper web 20 threads the space between the hammer striking faces 22 and the surface of the drum l2. Additionally, the printing ribbon 24 is disposed between the paper web 20 and the drum surface. The paper web 20 is normally provided with edge perforations (not shown) adapted to be engaged with fingers 26 formed on a tractor chain 28. The tractor chain 28 is driven by a gear 29 which in turn may be belt driven by a motor responsive to signals provided by paper control circuitry (not shown). Suitable paper drive systems are disclosed in greater detail in U. S. Pat. Nos. 3,423,658 and 3,452,853.

In the normal operation of the line printer 10 of FIG. 1, the paper web 20 is stepped one line at a time in the direction of the arrow 32 at rates up to about 2,000 lines per minute. When the paper web 20 is at rest between successive movements, a full line can be printed, normally in one full rotation of the drum 12. That is, in one full rotation of the drum 12, a full set of characters will move past the striking face 22 of each of the hammers 16. By impacting a hammer 16 against the drum 12 when the desired character is in alignment therewith, that character will be printed on the surface of the paper web 20 adjacent to the ink ribbon 24. Although various hammer structures are known in the art, a particuarly suitable hammer structure is disclosed in U. S. Pat. No. 3,279,362.

In order to achieve good registration of the characters in a single line, it is essential that the paper web 20 be held fixed and flat while all of the characters in that line are to be printed. Thus, after the paper web 20 has been stepped from one line to the next, it is necessary to allow some time for the paper web 20 to settle before printing is initiated. The amount of time which is allowed for settling, of course, has a direct affect on the print line rate. For a given apparatus, reduction of the settling time duration beyond a certain point will result in degraded print quality because if the paper web 20 is moving during printing, the printed characters may be misaligned. Thus, the characteristics of the paper drive system, as well as the characteristics of the hammers 16, bear directly on the print line rate and as a consequence, significant efforts have been made in the prior art to maximize the operating speed of both the paper drive system and hammers l6.

In a continuing effort to improve print quality, including precise registration of characters along a single line, an additional problem has been encountered as a consequence of slight paper movement produced by the drum 12 dragging the paper web 20 during the initial impact of a hammer 16 on a line. More particularly, as a practical matter, a certain degree of compliance and backlash exists in all paper web 20 drive systems. Thus, after the paper has been stepped to a new line and settled, it is normally still possible to slightly pull the paper web 20 downwardly, taking up some of the compliance in the paper drive system. As a consequence of this characteristic, upon the initial impact of a hammer 16 on a line, the motion of the drum surface acting on the paper web 20 often slightly pulls the paper web 20 downwardly so that subsequent characters printed on the same line will be printed high. As previously pointed out, prior efforts have been made to clamp paper web 20 to prevent this movement but such efforts have primarily utilized relatively slow acting and small motion solenoid devices. Where paper clamp devices are utilized, time must of course be allowed in a printing cycle to allow for the clamping, releasing and clearing actions. If the clamping device is slow acting, it can substantially increase the print cycle time and therefore correspondingly decrease the print line rate. If it does not release and clear, then paper web 20 may jam or smear during advance. If the clamp impacts against the paper web 20 with sufficient force, it will mark the paper web 20 and be noisy. The present invention is primarily directed to an improved means for controllably clamping a web, such as paper web 20 in a high speed impact printer 10.

More particularly, a clamping device 40 in accordance with the present invention, is preferably mounted downstream (and/or upstream) from a printing station in the printer 10, of FIG. 1. As shown in FIGS. 1, 2, and 3, the clamping device 40 is comprised of a flat coil structure 42 which includes a rigid elongated frame 44. The frame 44 has long front and rear edge surfaces 46 and 48 and relatively short end surfaces 50 and 52. A multiturn conductor coil 54 is housed within the coil structure 42 between top and bottom plates 56 and 58. The coil structure 42 preferably includes a central cutout area 60 to reduce the coil structure mass. A pressure bar 62 is securely fixed to the coil structure front edge surface 46.

As is best shown in FIG. 1, the coil structure 42 is supported by front and rear flexure members 64 and 66 depending from magnetic structural members 68. The flexure members 64 and 66 preferably comprise leaf springs and, as shown, support the coil structure 42 in an essentially horizontal plane extending substantially perpendicular to the plane of the paper web 20. A pressure plate 70 is mounted in alignment with the pressure bar 62 but on the opposite side of the path of paper web 20. By moving the coil structure 42 forwardly toward the pressure plate 70, the paper web 20 will be clamped and held therebetween.

In accordance with the present invention, the coil structure 42 is mounted in a magnetic field produced by permanent magnets. The permanent magnets can comprise unitary U-shaped structures or can be formed, as shown in FIG. 1, by bar magnets 74 and 76 mounted on a magnetic support member 68. Similarly,

magnets 78 and 80 are mounted on a second magnetic support member 82. The magnet configuration produces a magnetic flux path generally represented by the dash line 84 which extends across the gaps between magnets 74 and 78 and between magnets 76 and 80. As should be readily apparent, by driving a current through the coil 54 within the coil structure 42, a force will be developed on the coil structure 42 in a direction tending to move it within a plane defined by the coil structure 42 or in other words toward the pressure plate 70.

Attention is now called to FIGS. 4 and 5 of the drawing which illustrate a suitable control circuit 90 for developing a drive current for application to the coil 54. As will be more readily understood hereinafter, the circuit 90 comprises a closed loop circuit which enables the coil structure 42 to be controllably linearly displaced from the' quiescent release position shown in FIG. 1 to a clamp position in which the pressure bar 62 clamps the paper web against the pressure plate 70.

Prior to considering the control circuitry 90 of FIG. 4, attention is called to lines (a) and (b) of FIG. 5 which respectively illustrate waveforms associated with a typical paper feed system. Line (a) of FIG. 5 represents a command signal provided to the paper feed motor in order to step the paper web 20 one line. In response to the paper feed command signal of line (a), the paper web 20 is moved in a manner represented by the velocity waveform of line (b). Note that the paper velocity is linearly increased from rest, represented by base line 100 to some maximum velocity represented by level 102. Once the paper web 20 approaches its destination position, the paper velocity is linearly reduced, shown by sloped line 104, so that the paper velocity reaches zero, represented by base line 106, concurrent with the arrival of the paper web 20 at its destination position. A more thorough description of the paper feed system and the paper velocity waveform of line (b) of FIG. 5 is discussed in the aforecited U. S. Pat. No. 3,452,853. In accordance with the present invention, the'paper feed input signal of line (a) of FIG. 5 is applied to the input of a control logic means 108 of the control circuit 90 of FIG. 4. In addition, a position pulse, developed by the paper feed system discussed in US. Pat. No. 3,452,853, used to initiate the deceleration of the paper velocity, is also applied to the input of the control logic means 108.

The leading edge 110 of the paper feed input signal (FIG. 5, line (a) initiates paper movement and in addition, in accordance with the present invention, is utilized by the circuit 90 of FIGQ4 to move the pressure bar 62 on the clamping device 40 from the clamp to the release position. More particularly, in response to the leading edge 110 of the paper feed input signal, a release command pulse 114 (FIG. 5, line (c) is developed on the control logic output terminal 116. Tenninal l 16 is connected to the input of a command generator circuit 118. As shown in line (e) of FIG. 5, in response to the leading edge 120 of the release command pulse 114, the command generator 118 produces an output signal of increasing amplitude as represented at 122. In response to the trailing edge 124 of the release command pulse 114, the command generator output decreases toward zero represented by line 126. As will be seen hereinafter, the positive and negative going excursions 122 and 126 of the command generator output act respectively to accelerate the coil structure 42 rearwardly and to then decelerate the coil structure 42 so that its velocity is reduced to substantially zero coincident with its arrival at the quiescent release position illustrated in FIG. 1.

In response to the position pulse supplied to the input of the control logic means 108, a hold command pulse 130 (FIG. 5, line (d) is developed by the control logic 108 on output terminal 131. The leading and trailing edges 132 and 136 of the pulse 130 produce negative and positive going excursions 134, 138 respectively in the command generator output signal (FIG. 5, line (e) As will be seen hereinafter, the effect of the negative and positive going excursions 134 and 138 in the command generator output signal is to initially accelerate the coil structure 42 in a forward direction toward the pressure plate 70 and to then reduce the forward velocity to zero substantially coincident with the engagement of the pressure bar 62 against the pressure plate 70.

The output of the command generator 118 is applied through a resistor 140 to a summing junction 142 at the input of an error amplifier 144. The output of the error amplifier 144 is supplied to a power amplifier 146 which develops a current for application to the conductor coil 54 of the coil structure 42. In order to produce a coil structure velocity corresponding to that represented by the output of the command generator 118, a velocity transducer 150 is provided to develop a velocity signal which is then fed back to the summing junction 142 of the error amplifier 144. The details of the preferred velocity transducer embodiment will be discussed hereinafter but suffice it to say at this point, the signal produced by the velocity transducer 150 is coupled through a switch 152 and a resistor 154 to the summing junction 142. The switch 152 is controlled by an output terminal 156 of the control logic means 108 so that it is enabled (FIG. 5, line (i) during the entire paper feed sequence illustrated in FIG. 5. As a consequence of providing a closed loop circuit 90 in which a signal representative of coil structure velocity is summed with the command generator output signal, the velocity of the coil structure 42 will indeed correspond to that represented by the generator output signal of FIG. 5, line (e). It should be appreciated from the waveform that the velocity of the coil structure 42, both for forward movement to the clamp position and for rearward movement to the release position, will be reduced to zero substantially coincident with the arrival of the coil structure 42 at the respective positions thereby assuring quiet operation of the clamping device 40. More significantly, however, the clamping device 40 will operate quite rapidly since the coil structure 42 will settle immediately upon arrival at its destination position.

In order to assure that the coil structure 42 is held tightly against pressure plate 70 when in its clamp position, a bias current (FIG. 5, line (h) is supplied to the coil 54 by the control logic means 108. More particularly, the hold bias current 170 is supplied at all times except during the paper feed sequence which is initiated coincident with the leading edge 110 of the paper feed input signal and terminated coincident with the forward velocity of the coil structure 42 being reduced to zero. Thus, at all times other than when the paper web 20 is being moved, the coil structure 42 will be clamped against the pressure plate 70 as a consequence of the hold bias current 170 supplied to the summing junction 142 via the resistor 172. A release bias current 176 (FIG. 5, line (g) opposite in polarity to the hold bias current 170 is applied to the coil 54 during the paper feed sequence of FIG. via resistor 178 coupled to the summing junction 142. Line (f) of FIG. 5 illustrates the current through the coil 54 produced as a consequence of the sum of the various signal components supplied to the summing junction 142.

Attention is now again called to FIGS. 1-3 which illustrate a particularly useful velocity transducer embodiment for developing the coil structure velocity signal fed back through switch 152 to the summing junction 142. The velocity transducer 150 comprises a coil 180 physically secured to the coil structure 42. As the coil structure 42 moves, the coil 180 correspondingly moves within a gap defined by an upper pair of permanent magents 182 and 184 and a lower pair of permanent magnets 186 and 188. The permanent magnets 182, 184, 186, and 188 produce flux along a path represented by the dash line 190 shown in FIG. 3. It should be readily recognized as the conductor of coil 180 cuts the flux lines produced by the permanent magnets 182, 184, 186, 188, it will develop an output signal related to the rate of change of flux. Consequently, the coil 180 will produce a signal at its output terminals representative of the velocity of coil 180 which, of course, is also the velocity of the coil structure 42. It is pointed out that the coil 180 is preferably mounted transverse to the coil 54, as illustrated in FIGS. 1-3, in order to minimize any inductive coupling therebetween.

From the foregoing, it should be recognized that a web clamping device 40 has been disclosed herein which can operate rapidly and quietly to selectively clamp the web in a web feed type apparatus, such as a high speed printer 10. Although a particular embodiment of the invention has been shown herein, it is recognized that variations and modifications within the scope of the invention may readily occur to those skilled in the art. For example only, although a single clamping device 40 has been illustrated in the drawing downstream from the print station, it may be preferable in some embodiments to employ clamping devices 40 both upstream and downstream from the print station. Further, although a flat fixed pressure plate 70 has been shown, the invention is also useful in embodiments where, for example, the pressure plate surface is other than flat and where the pressure plate 70 may be movable toward the coil structure 42. Still further, although the clamping device 40 has been disclosed for use in conjunction with a velocity servo loop, it should be recognized that alternatlvely, or additionally, coil structure position information can be fed back to thereby enable the. position of the coil structure 42 to be precisely controlled for establishing a desired force on the web 20.

What is claimed is: r

1. Apparatus suitable for clamping web material to prevent movement of said material, said apparatus comprising:

a planar coil structure having a clamping surface extending substantially the full length thereof, said coil structure including a conductor coil defining an axis extending perpendicular to the plane of said coil structure;

a fixed pressure plate mounted opposite to said coil structure clamping surface;

means supporting said coil structure in a quiescent position with said clamping surface spaced from said pressure plate for substantially linear movement in the plane defined thereby toward said pressure plate;

means producing a magnetic field extending across said conductor coil and parallel to the axis thereof;

means for generating a hold command signal;

means responsive to said hold command signal for driving a current through said conductor coil having a waveform shaped to initially accelerate said coil structure toward said pressure plate and to subsequently decelerate said coil structure to reduce the velocity of said coil structure to substantially zero coincident with said clamping surface engaging said pressure plate; and

means for producing a first polarity bias current in said conductor coil when said clamping surface is engaged with said pressure plate to produce a force on said coil structure urging said clamping surface against said pressure plate.

2. The apparatus of claim 1 wherein said means producing a magnetic field includes permanent magnets supported on at least one side of the plane of said coil structure.

3. The apparatus of claim 1 including transducer means responsive to said coil structure velocity for developing a feedback signal; and

wherein said means for driving a current through said conductor coil includes means responsive to said feedback signal.

4. The apparatus of claim 1 wherein said means supporting said coil structure includes a plurality of flexure members secured between said coil structure and a fixedly mounted base member.

5. The apparatus of claim 1 including:

means for generating a release command signal; and

means responsive to said release command signal for producing a second polarity bias current on said conductor coil to develop a force on said coil structure urging said coil structure away from said pressure plate.

6. Apparatus suitable for clamping web material to prevent movement of said material, said apparatus comprising:

a planar coil structure having a clamping surface extending substantially the full length thereof, said coil structure including a conductor coil defining an axis extending perpendicular to the plane of said coil structure;

a fixed pressure plate mounted opposite to said coil structure clamping surface;

means supporting said coil structure in a quiescent position with said clamping surface spaced from said pressure plate for substantially linear movement in the plane defined thereby toward said pressure plate;

means producing a magnetic field extending across said conductor coil and parallel to the axis thereof;

means for driving a current through said conductor coil to produce a force thereon acting to urge said coil structure to a forward position whereat said clamping surface engages said pressure plate for clamping web material therebetween;

said means for driving a current through said conductor coil including (1) means for generating a command signal (2) transducer means responsive to said coil structure for developing a feedback signal and (3) means responsive to said command and feedback signals for producing a drive signal for application to said conductor coil;

said transducer means for developing said feedback signal including a relatively small planar flat coil having terminals and mounted on said coil structure for movement therewith;

means for producing a magnetic field across said small flat coil extending substantially perpendicular to the plane of said small flat coil; and

means for obtaining said feedback signal from across the terminals of said small flat coil.

7. The apparatus of claim 6 wherein said small fiat coil is oriented with the plane of said small flat coil extending substantially perpendicular to the plane of said coil structure.

8. In a printer including means for incrementally feeding a paper web along a specified path, electrically actuatable clamping means for clamping said paper web to prevent movement thereof, said clamping means comprising:

a fiat rigid coil structure having a clamping surface extending substantially the full length thereof and including a conductor coil defining an axis extending perpendicular to the plane of said coil structure;

means supporting said coil structure for substantially linear movement in a plane defined thereby extending substantially perpendicular to the path of said paper web;

a fixed pressure plate mounted in alignment with said coil structure on the opposite side of said paper web path;

means producing amagnetic field extending across said conductor coil and parallel to the axis thereof;

means for generating a hold command signal;

means responsive to said hold command signal for driving a current through said conductor coil having a waveform shaped to initially accelerate said coil structure toward said pressure plate and to subsequently decelerate said coil structure to reduce the velocity of said coil structure to substantially zero coincident with said clamping surface engaging said pressure plate; and

means for producing a first polarity bias current in said conductor coil' when said clamping surface is engaged with said pressure plate to produce a force on said coil structure urging said clamping surface against said pressure plate.

9. The printer of claim 8 including a fixedly mounted base member; and wherein said means supporting said coil structure includes a plurality of flexure members secured between said base member and said coil structure.

10. The printer of claim 8 including a transducer means responsive to the velocity of said coil structure for developing a feedback signal;

amplifier means; and

means coupling said command and feedback signals to said amplifier means for producing a drive signal for application to said conductor coil.

11. The printer of claim 8 including:

means for generating a release command signal; and

means responsive to said release command signal for producing a second polarity bias current in said conductor coil to develop a force on said coil structure urging said coil structure away from said pressure plate.

12. In a printer including means for incrementally feeding a paper web along a specified path, electrically actuatable clamping means for clamping said paper web to prevent movement thereof, said clamping means comprising:

a fixed pressure plate mounted in alignment with said coil structure on the opposite of said paper web path;

means producing a magnetic field extending across said conductor coil and parallel to the axis thereof;

means for driving a current through said conductor coil to produce a force thereon acting to urge said coil structure clamping surface into engagement with said pressure plate for clamping said paper web therebetween; said means for driving a current through said conductor coil including 1) means for generating a command signal, (2) transducer means responsive to said coil structure for developing a feedback signal and (3) means responsive to said command and feedback signals for producing a drive signal for application to said conductor coil; said transducer means for developing said feedback signal including planar coil means having terminals and mounted on said coil structure for movement therewith for developing a velocity feedback signal; means for producing a magnetic field across said coil means extending substantially perpendicular to the plane of said coil means; and means for obtaining said velocity feedback signal from across the terminals of said coil means.

13. The printer of claim 12 wherein said coil means is oriented with the plane of said coil means extending 0 substantially perpendicular to the plane of said coil structure. 

1. Apparatus suitable for clamping web material to prevent movement of said material, said apparatus comprising: a planar coil structure having a clamping surface extending substantially the full length thereof, said coil structure including a conductor coil defining an axis extending perpendicular to the plane of said coil structure; a fixed pressure plate mounted opposite to said coil structure clamping surface; means supporting said coil structure in a quiescent position with said clamping surface spaced from said pressure plate for substantially linear movement in the plane defined thereby toward said pressure plate; means producing a magnetic field extending across said conductor coil and parallel to the axis thereof; means for generating a hold command signal; means responsive to said hold command signal for driving a current through said conductor coil having a waveform shaped to initially accelerate said coil structure toward said pressure plate and to subsequently decelerate said coil structure to reduce the velocity of said coil structure to substantially zero coincident with said clamping surface engaging said pressure plate; and means for producing a first polarity bias current in said conductor coil when said clamping surface is engaged with said pressure plate to produce a force on said coil structure urging said clamping surface against said pressure plate.
 2. The apparatus of claim 1 wherein said means producing a magnetic field includes permanent magnets supported on at least one side of the plane of said coil structure.
 3. The apparatus of claim 1 including transducer means responsive to said coil structure velocity for developing a feedback signal; and wherein said means for driving a current through said conductor coil includes means responsive to said feedback signal.
 4. The apparatus of claim 1 wherein said means supporting said coil structure includes a plurality of flexure members secured between said coil structure and a fixedly mounted base member.
 5. The apparatus of claim 1 including: means for generating a release command signal; and means responsive to said release command signal for producing a second polarity bias current on said conductor coil to develop a force on said coil structure urging said coil structure away from said pressure plate.
 6. Apparatus suitable for clamping web material to prevent movement of said material, said apparatus comprising: a planar coil structure having a clamping surface extending substantially the full length thereof, said coil structure including a conductor coil defining an axis extending perpendicular to the plane of said coil structure; a fixed pressure plate mounted opposite to said coil structure clamping surface; means supporting said coil structure in a quiescent position with said clamping surface spaced from said pressure plate for substantially linear movement in the plane defined thereby toward said pressure plate; means producing a magnetic field extending across said conductor coil and parallel to the axis thereof; means for driving a current through said conductor coil to produce a force thereon acting to urge said coil structure to a forward position whereat said clamping surface engages said pressure plate for clamping web material therebetween; said means for driving a current through said conductor coil including (1) means for generating a command signal (2) transducer means responsive to said coil structure for developing a feedback signal and (3) means responsive to said command and feedback signals for producing a drive signal for application to said conductor coil; said transducer means for developing said feedback signal including a relatively small planar flat coil having terminals and mounted on said coil structure for movement therewith; means for producing a magnetic field across said small flat coil extending substantially perpendicular to the plane of said small flat coil; and means for obtaining said feedback signal from across the terminals of said small flat coil.
 7. The apparatus of claim 6 wherein said small flat coil is oriented with the plane of said small flat coil extending substantially perpendicular to the plane of said coil structure.
 8. In a printer including means for incrementally feeding a paper web along a specified path, electrically actuatable clamping means for clamping said paper web to prevent movement thereof, said clamping means comprising: a flat rigid coil structure having a clamping surface extending substantially the full length thereof and including a conductor coil defining an axis extending perpendicular to the plane of said coil structure; means supporting said coil structure for substantially linear movement in a plane defined thereby extending substantially perpendicular to the path of said paper web; a fixed pressure plate mounted in alignment with said coil structure on the opposite side of said paper web path; means producing a magnetic field extending across said conductor coil and parallel to the axis thereof; means for generating a hold command signal; means responsive to said hold command signal for driving a current through said conductor coil having a waveform shaped to initially accelerate said coil structure toward said pressure plate and to subsequently decelerate said coil structure to reduce the velocity of said coil structure to substantially zero coincident with said clamping surface engaging said pressure plate; and means for producing a first polarity bias current in said conductor coil when said clamping surface is engaged with said pressure plate to produce a force on said coil structure urging said clamping surface against said pressure plate.
 9. The printer of claim 8 including a fixedly mounted base member; and wherein said means supporting said coil structure includes a plurality of flexure members secured between said base member and said coil structure.
 10. The printer of claim 8 including a transducer means responsive to the velocity of said coil structure for developing a feedback signal; amplifier means; and means coupling said command and feedback signals to said amplifier means for producing a drive signal for application to said conductor coil.
 11. The printer of claim 8 including: means for generating a release command signal; and means responsive to said release command signal for producing a second polarity bias current in said conductor coil to develop a force on said coil structure urging said coil structure away from said pressure plate.
 12. In a Printer including means for incrementally feeding a paper web along a specified path, electrically actuatable clamping means for clamping said paper web to prevent movement thereof, said clamping means comprising: a flat rigid coil structure having a clamping surface extending substantially the full length thereof and including a conductor coil defining an axis extending perpendicular to the plane of said coil structure; means supporting said coil structure for substantially linear movement in a plane defined thereby extending substantially perpendicular to the path of said paper web; a fixed pressure plate mounted in alignment with said coil structure on the opposite of said paper web path; means producing a magnetic field extending across said conductor coil and parallel to the axis thereof; means for driving a current through said conductor coil to produce a force thereon acting to urge said coil structure clamping surface into engagement with said pressure plate for clamping said paper web therebetween; said means for driving a current through said conductor coil including (1) means for generating a command signal, (2) transducer means responsive to said coil structure for developing a feedback signal and (3) means responsive to said command and feedback signals for producing a drive signal for application to said conductor coil; said transducer means for developing said feedback signal including planar coil means having terminals and mounted on said coil structure for movement therewith for developing a velocity feedback signal; means for producing a magnetic field across said coil means extending substantially perpendicular to the plane of said coil means; and means for obtaining said velocity feedback signal from across the terminals of said coil means.
 13. The printer of claim 12 wherein said coil means is oriented with the plane of said coil means extending substantially perpendicular to the plane of said coil structure. 